​ NachtWal (ナハトヴァール Nahato Vāru) is the materialisation (実体化 jittaika) of the Defense Program of the Book of Darkness. The Book, originally known as the "Tome of the Night Sky" before it was corrupted, was a Lost Logia Unison Device: an intelligent creation of Ancient Belkan mages whose names have been lost to time. Its final master, Hayate Yagami, had reprogrammed it and separated the Defense Program from other components.